Quest for African AIDS Vaccine Hampered by Focus, Virus Mutation

Researchers in Burkina Faso at the conference on AIDS in Africa heard evidence that the search for a vaccine to fight HIV on the continent is being clouded by a focus on viral sub-types predominant in the West and by the virus' ability to mutate.

Two-thirds of the world's 40 million HIV-positive people live in sub-Saharan Africa. The predominant sub-types of HIV-1 -- by far the most prevalent and vicious of the two known major strains of the virus -- are A in eastern Africa; C in southern Africa and the Horn of Africa; and mixed A/G in western and central Africa. But of the vaccines in trials today, 70 percent are modeled on the genetic profile of sub-type B, which predominates among HIV patients in the United States. Only 3 percent address the sub-types of the African epidemic. "HIV vaccines should be designed for effectiveness in sub-Saharan Africa," said Harvard University vaccine expert Max Essex. "Any vaccine that works must be made available first, or concurrently, in sub-Saharan Africa."

"The truth is that we do not know whether a vaccine designed for one kind of sub-types will work on another, or if so what its effectiveness will be," said Eric Delaporte, a virologist at France's Research Institute for Development. "In vitro, it appears to work, but there has been no confirmation in vivo, and of course we still do not know about the results on humans." Only one candidate vaccine, gp120 (AIDSVAX), has made it to Phase III trials.

Adding to the problem is the remarkable ability of viral sub-types to swap genes, fueling fear that HIV could become a moving target for vaccine engineers. "Recombinant viruses contribute to 10-30 percent of the global pandemic," said Soleymane M'Boup of Senegal, the discoverer of HIV-2. "The frequency of subtypes will increase." Delaporte said that once an effective vaccine is found, it should be possible to deal with new recombinants in the same way scientists tweak flu vaccines to deal with new sub-strains. "But this requires good epidemiological infrastructure," he said, which means tracking newly emerging recombinant strains.

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